Nonlinear interactions of two ultrasonic waves, propagating collinearly in a dispersionless liquid medium, are investigated experimentally for both degenerate and nondegenerate cases. Results are described of the first experimental observation of parametric amplification of the signal wave for the degenerate case. For the nondegenerate case, no such amplification of the amplitude of the signal wave is observed. These experimental results are found to be in good agreement with the results of the theoretical analysis presented in the paper.